1. Field of the Invention
The present invention relates to switch devices.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 2007-283471 discloses a known switch used for an impact screwdriver having a rechargeable battery. For this type of impact screwdriver, there has been used a switch as shown in FIGS. 5(A) and 5(B). A switch 100 shown in these figures include a switch body 101 and a operation member 103. The switch body 101 includes a cylindrical tubular case 101c and a rotary shaft 101j. A switch circuit (not shown) is disposed within the case 101c. The rotary shaft 101j is coaxially rotatably supported by the case 101c and extends in an axial direction from one end of the case 101c. The switch circuit is operated as the rotary shaft 101j rotates about its axis relative to the case 101c. 
An operation member 103 surrounds the case 101c of the switch body 101 and is supported to be coaxial with the case 101c. One end of the operation member 103 is joined to the leading end portion of the rotary shaft 101j not to rotate relative thereto. Therefore, it is possible to rotate the rotary shaft 101j relative to the case 101c by operating the operation member 103. A pair of linier protrusions 103t for engaging fingers of a user are formed on the outer circumferential surface of the operation member 103 and extend in the axial direction.
As described above, one end in the axial direction of the rotary shaft 101j of the switch body 101 and one end in the axial direction of the operation member 103 are joined to each other. Therefore, when a pressing force is applied to a portion of the operation member 103 positioned between the central position and the other end during the operation of the operation member 103, a torsional force is applied to a joint portion between the operation member 103 and the rotary shaft 101j as indicated by arrows in FIG. 5(A), and therefore, it may be possible that the joint portion is loosened during the long time use.
This loosening of the joint portion may be prevented, for example, by providing a ring-shaped projection 105 that extends radially inwardly from the inner wall surface of the operation member 103 as shown in FIGS. 5(C) and 5(D). The inner circumferential edge of the projection 105 may contact the outer circumferential surface of the case 101c of the switch body 101, so that a middle portion with respect to the axial direction of the operation member 103 is supported by the projection 105. Therefore, it may be possible to prevent or inhibit application of the torsional force to the joint portion between the rotary shaft 101j and the operation member 103.
However, in the case of the arrangement shown in FIGS. 5(C) and 5(D), dust or cut powder may be clogged within a clearance between the inner circumferential edge of the projection 105 and the outer circumferential surface of the case 101c to prevent the operation member 103 (or the projection 105) from smoothly sliding relative to the case 101c. 
Therefore, there is a need in the art for a switch that has a dust-proof performance and is improved in operability of an operation member